Orrego-Salas was born in Santiago, Chile, in January 1919. He began his initial education and training as a musician in his native city, later studying and obtaining his diploma in architecture in 1943. By that time, he had completed his undergraduate work in composition with Pedro Humberto Allende and Domingo Santa Cruz, and was teaching history and literature of music at the Universidad de Chile and conducting the Universidad Católica de Chile, which he established in 1938. He studied composition with Aaron Copland in Tanglewood and at the universities of Virginia and Princeton with Randall Thompson, as well as musicology with Paul Henry Lang and Georg Herzog at Columbia University. In 1947, he returned to his home country as full music faculty professor of the Universidad de Chile and as choral conductor at the Universidad Católica. In 1950 became the music critic of El mercurio, Chile's leading morning paper. An uninterrupted dedication to composition resulted in continuous performances of his works in Chile and abroad; he received many commissions to write compositions for orchestra and a variety of chamber ensembles. In 1953, the Universidad de Chile conferred upon him the title of Profesor Extraordinario (Distinguished Professor) of composition, and the following year he returned to the United States and spent a year composing in New York, making use of a second Guggenheim Fellowship. He then returned to Chile to become the director of the Instituto de Extensión Musical, the organization under whose leadership the Orquesta Sinfónica de Chile, the Ballet Nacional Chileno, and a number of choral and chamber ensembles operated. After two years in this position he resigned to become the founder and first director of the Departamento de Música (now Instituto de Música) of the Universidad Católica in Santiago. He remained in this position until 1961 and after a twenty-year career as a member of the music faculty of the Universidad de Chile, he was granted a partial retirement and returned to the United States, this time to establish and direct the Latin American Music Center and teach composition at the School of Music of Indiana University, in Bloomington. After serving twenty-seven years at Indiana University, including a period between 1975 and 1980 as chairman of the composition department, he retired in 1987 as “Professor Emeritus.” As a teacher and lecturer, he appeared in many universities, colleges, and cultural institutes in Chile and the United States, as well as in Argentina, Brazil, Colombia, France, Great Britain, Italy, Mexico, Peru, Russia, Spain, Uruguay, Venezuela, and the former Yugoslavia, and he participated in several international meetings.